Method of producing wheel and the wheel

ABSTRACT

A method of producing a light alloy wheel with a forging technique, aiming for producing the wheel having a large-diameter disk by use of a small-scale press device, comprising: heating an intermediate product that is formed by casting or forging and has a discoid and a cylindrical thick wall, which are to respectively become disk and rim at completion, to a plasticity temperature; then, rotating the intermediate product with stopping of the rotating at interval of a predetermined angle; pressing at least a portion of the to-be disk part by molds at time of said stopping, as to push out metal into recesses on the lower mold and to thereby form holes; repeating of such rotating, stopping and pressing as to give a pattern on whole of the to-be disk part; and further press processing and finish processing on the to-be disk and the to-be rim parts.

FIELD OF THE INVENTION

This invention relates to a method of producing wheel formed oflightweight metal for a vehicle as well as such wheel.

BACKGROUND OF THE INVENTION

The wheels formed of lightweight metal that are preferably used inpassenger automobiles greatly contribute for decreasing load underneaththe springs and for improving maneuverability and fuel efficiency ormileage. Such wheels are produced by casting or forging as to provideones having excellent ornamental appearances. In response to quest forwheels more lightweight and more excellent in the ornamentalappearances, the lightweight metal wheels allegedly have a shareexceeding 60% in wheels for the passenger automobiles. With increase ofspeed capacity of the passenger automobile, there is requiredenlargement of brake mechanism and of the wheel; thereby, diameter ofthe wheels increases year by year and may well soon exceed 17 inch innowadays trend.

In producing the lightweight metal wheels, aluminum or magnesium ismainly used as material for the wheel, and the forging is preferablyused in order for achieving densely packed metallographic structure andthereby for enhancing stiffness of the metal.

Method of the forging in prior art is exemplarily shown byJP-1985(S60)-127040A (Prior-Art Patent Document 1), which shows a methodcomprising of; a step of forging a disc-shaped work having thick-wallouter fringes; a step of forge-wise forming, from the disc-shaped work,a disk part having edges in predetermined shape and relief-wise formedpredetermined window openings as recesses, or such disk part and a ringpart integrally continuous with the disk part; a step of cutting outbottoms of the recesses as to form window openings; and a step ofchamfering inner peripheral fringe of the window openings.

If diameter of the disk is less than about 18 inch, a press devicehaving capacity of about 8000 metric ton is enough for pressing wholeface of the disc. If the diameter of the disk exceeds the 18 inch, it isdifficult to press the whole face of the disk by use of the press deviceof about 8000 metric ton capacity and thereby press device of about10,000 metric ton capacity is needed.

Portion-by-portion stepwise forging technique has been known as forforging a member having large area by use of a small-scale press device.As for forming a disk of simple shape by such technique,JP-1983(S58)-12092A (Prior-Art Patent Document 2) for example shows amethod for forging a beam flange for warping of yarns; in which astarting metal piece is portion-by-portion stepwise pressed as to omit aneed of large-scale pressing device; and in which then obtained disk isprogressively enlarged by properly changing upper mold. By this method,the flange having diameter of 30 inch or more may be obtained, while no“pattern” may be formed because the disk is drawn not only in acircumferential direction but also in a radial direction on course ofthe stepwise pressing.

Other than the portion-by-portion stepwise forging technique, rotationforging technique has been known and proposed by numerous prior-artdocuments. In principle, a tool having conical face is tilted andabutted on a work and the forming is gradually and successively made incircumferential direction by such way of pressing. Typical methods inthe rotation forging technique are shown in JP-1994(H06)-154932A(Prior-Art Patent Document 3) and JP-1994(H06)-285575A (Prior-Art PatentDocument 4).

In the method shown in JP-1994(H06)-154932A, a work that has ato-be-disk part and a to-be-rim part protruded in a ring shape fromperiphery of the disk part is prepared; and then the work is rotated andat same time compressed by a lower tool for processing outer face of theto-be-disk part and an upper tool for processing inner face of theto-be-disk part, while the to-be-rim part is abutted by a formingroller, as to form an integral wheel. In the method shown inJP-1994(H06)-285575A, a set of upper and lower tools in which concaveand convex portions are alternately formed along a circle line with aconstant amplitude is used; and firstly, one of the concave portions isaligned with one of the convex portions and then pressing is made, andsuch forge processing is made along a whole circle by rotating the toolsas from such firstly aligned position. In such rotation forgingtechnique, material of the work is migrated in radially outwarddirections. Thus, a disk pattern stretched in a radial direction may beformed whereas more complicated “pattern” is not achievable.

SUMMARY OF THE INVENTION

In view of the above, it is aimed to provide a method in the forgingtechnique for manufacturing a wheel formed of a light alloy and having alarge diameter by use of a small-scale press device.

Invention-wise process for manufacturing a vehicle's wheel formed oflightweight metal comprising; heating an intermediate product that isformed by casting or forging and has a to-be disk part and a to-be rimpart, to a plasticity temperature; then, rotating the intermediateproduct with stopping of the rotating at interval of a predeterminedangle; pressing at least a portion of the to-be disk part by molds orforming tools at time of said stopping; repeating of such rotating,stopping and pressing as to give a disk-part pattern on whole of theto-be disk part; and further press processing and finish processing onthe to-be disk and the to-be rim parts as to form disk and rim parts.

The plasticity temperature at above is a temperature at which plasticdeformation is easily made by pressing. For lightweight metal such asaluminum and magnesium, the plasticity temperature is preferably in arange of 420-450° C. When nominal diameter of the wheel is no less than18 inch, the diameter of the disk is no less than 17 inch. When to formthe “pattern” en bloc by pressing whole surface of the disk part in sucha diameter in forge processing, a press device of about 8000-toncapacity is needed. Such a large-scale press device is expensive andrequires an accordingly sizable place for installing the device. Thus,it is desirable when press device having smaller scale is adoptable inproducing a disk of a large diameter.

The invention-wise process enables producing of a disk having largediameter by stepwise forging, by use of a press device of smaller scalecompared to fore-mentioned ones; for example by use of a press devicehaving a capacity in a range of 1000 through 4000 ton, although requiredcapacity may vary depending on a size of area that is pressed at a timeof the stopping.

The intermediate product may be formed by pressing a billet as to form aconvex-part making a hub at a center of the billet as well as a discoidat around the hub, and to have a cylindrical tube of thick wall as theto-be rim part at periphery of the discoid. Such intermediate productmay be formed by expanding with successive change of tools by use of asmall-scale press device because no surface “pattern” is to be formed onthe discoid.

The intermediate product may be molded by casting. In general, avertical thrust force is applied in the press device; hence, a formingtool applying the thrust force will be preferred as upper mold and theother forming tool will be preferred as lower mold.

A disk of 17 inch diameter has an area in a range of 1300 through 1600cm². Thus, when assumed as about 4 ton per square centimeter of pressingforce is needed for forming a disk-part pattern by pressing, a pressdevice of about 6000-ton capacity is needed, in a rough estimation. Whena press device of about 3000-ton capacity is used, the pressing force isnot enough to apply pressing on whole of the disc. For this reason,stepwise and portion-wise forging is adopted.

Ornamental pattern on the disk of the wheel is given by forming holes onthe disk. For achieving a mass-wise balance in respect of rotation,holes having same configuration are arranged in a constant interval,which interval makes one pitch of the portion-by-portion-wise forging.The upper mold is provided with one or more projections matching theconfiguration of the holes. As far as afforded with capacity in pressingforce, plurality of the projections is formed on the upper mold. To copewith material flow due to free forging, recesses or holes are providedon the lower mold.

The lower mold has a configuration for fixing up the intermediateproduct so as not freely rotatable by holding the circular tube of theintermediate product from outside. The lower mold has a controller forindicating rotational angle so that rotating and its stopping of thelower mold is repeated in accordance with every pitch of the disk-partpattern. At time of the stopping, the upper mold is descended, and thusmaterial to be pushed out at the pressing moves downward.

The upper mold presses an area slightly larger than the one pitch of thedisk-part pattern, by a uniform pressing force all over the intermediateproduct. For replacing of the upper mold, it is preferred that aplurality of the upper mold are held or latched as slidable in ahorizontal direction as shown in the JP-1983(S58)-12092A (Prior-ArtPatent Document 2). Detail of the press device will be described later.

When to form holes comprising the disk-part pattern on the disk byportion-by-portion forging, it is not desirable that material at pressedportion expanded to its surroundings. Thus, ridges of mold's projectionson portions for abutting peripheries around the holes are shaped asrounded or as sharp-angled ridges of 90 degree or sharper angle.

For example, at portions for forming spokes, ridges on the projectionsare shaped as rounded, and thereby slight bulging of material is made,as to leave faces appeared as if being forge-wise pressed. Recesses areformed on a mold part that abuts the to-be rim part at regions otherthan its joints with the spokes; and an air valve is attached to aportion of walls of the recesses.

When to form through holes, the upper mold having sharp-angled ridges onthe projections is used for curbing flow of material at the throughholes toward the to-be rim part. The upper mold for forming the recesseshas protrusions having sharp-angled edges on a part of corners andhaving rounded faces on remaining corners, as to push out materialtoward the through holes in order for preventing material flow ormigration toward the rim part. At finishing step, molds having a shapematching completed product are used for the forming.

When to form the holes that make a disk-part pattern, two or threevarieties of the molds are used and changing of the mold is facilitatedby hanging the molds from rails that are arranged on an end of the pressdevice on its pressing side, as to decrease time required for changingthe upper, molds. Detail of the press device will be described in theembodiment. Ridges along the recesses or the through holes on the lowermold at places matching the sharp-angled ridges of the projections onthe upper mold are shaped as the sharp-angled ridges as in same manner,for cutting the material.

The intermediate product having been provided with the disk-part patternon the discoid is processed on a cylindrical thick wall around thediscoid, by spinning technique, as to form a rim. A method for suchprocessing is as follows as shown in Japanese registered Patent No.1769730 issued to the present applicant company; a mandrel havingundulation that matches holes on the disk-part pattern is used; theintermediate product is rotated while the disk is held as sandwiched,and a roller is abutted with a force on the intermediate product as toform the rim in a predetermined shape.

In this way, by a small-scale press device for forging a wheel, a wheelof lightweight alloy is completed which has a disk having diameter of 17inch or more and having an arbitrary disk-part pattern.

In the above method, the holes are formed by punching as to form adisk-part pattern, whereas also adopted is a method comprised of;forming a pre-press hole or “waste hole” (which means an additional holeprepared on beforehand of the pressing by the molds) with an areaslightly smaller than one of the holes to be formed; then a projectionon the lower mold is fitted into the “waste hole” as a fit-in orcatching hole; and a pressing is made on the to-be rim part and to-bedisk part, in a state sealed off from outside.

Please see a wheel having Y-shaped spokes on FIG. 3. When nominaldiameter that usually measures a diameter of the bead seat is 18 inch,diameter of outer fringe of the outer rim is about 498 mm. Thus, an areain a plan view is estimated as 1947 cm², total area of holes in the diskis 713 cm², and thus, aperture ratio on the disk is; 713/1947=36.6%.

When the waste hole is smaller than each side of the hole by about 5 mm,aperture area is 490 cm², and thus, aperture ratio on the disk is;490/1947=25.2%. Pressing force needed for the forging of the lightweightalloy in the sealed off state is 4 ton/cm² in a rough estimate that ismade on basis of past results. Multiplying of the 4 ton/cm² with thearea in the plan view gives 7788 ton; in this reason, the press deviceof 8000-ton capacity has been required. The waste holes alleviatesrequired pressing force by about 25%, then the press device of about6000-ton capacity is still required. In other words, only the pressdevice of about 6000-ton capacity has enabled forging or press-formingof the 18-inch wheel.

In invention-wise process, a projection on the lower mold is fitted intothe waste hole; then, the press device of 3000-ton capacity is used forthe forging in the sealed off state; and, an upper mold of dividedstructure is used for the portion-by-portion-wise forging when to presson whole of the to-be rim and to-be disk parts.

Providing the holes on the wheel is effective in decreasing weight ofthe wheel though extent of the decreasing depends on size of the holes;and the aperture ratio of 25% may be rather small. Mass correspondingthe waste holes is not included in the mass of the completed productthus required amount of the lightweight metal is increased, however,metal fragments resulted from punching may be reused.

By the invention, a 17-inch or larger wheel formed of lightweight metaland having stiffness and any disk-part pattern may be obtained by asmall-scale press device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a)-1(c) are vertical sectional views showing an intermediateproduct and molds in the first embodiment of the invention, FIG. 1( a)shows a state the upper mold is placed above the intermediate product,FIG. 1( b) shows a state the upper mold moves down and thrust-wisepunches holes on the discoid, and FIG. 1( c) shows an intermediateproduct after the processing in respect of the holes;

FIGS. 2( a)-(b) are perspective views showing positional relationshipbetween the upper mold and a wheel, FIG. 2( a) shows the upper mold seenfrom below and FIG. 2( b) shows the wheel;

FIG. 3 is an explanatory view of the wheel, showing range or area ofeach of the portion-by-portion-wise forging strokes;

FIGS. 4( a)-(d) show a manner of forming depressions for the wheel onthe FIG. 3, FIG. 4( a) is an explanatory view showing a range or area ofone stroke of forming procedure, FIGS. 4( b) and 4(c) are sectionalviews showing processes of the forming, and FIG. 4( d) is a sectionalview showing a portion having the depression at its completion;

FIG. 5 is an explanatory view showing another embodiment of providingwaste holes;

FIG. 6 is a sectional view showing a state of forming the rim by thespinning;

FIG. 7 is a partial elevational view of a pre-wheel in which waste holesare punched, in second embodiment;

FIGS. 8( a)-(d) are sectional views showing a process for forming thewheel in the second embodiment, FIG. 8( a) shows a pre-wheel, FIG. 8( b)shows the pre-wheel at a state the waste holes are punched, FIG. 8( c)is an explanatory sectional view schematically showing a pressingprocess, and FIG. 8( d) shows an intermediate product after the pressforming;

FIGS. 9( a)-(d) are explanatory views for showing manner of forging inthe second embodiment, FIG. 9( a) is a partial elevational view of thepre-wheel in which the waste holes are punched, and FIGS. 9( b)-9(d) aresectional views at A-A′ section of the FIG. 9( a) for showing a courseor process of the press forming; and

FIG. 10 is a side view of the press device for explaining a manner ofchanging the upper mold, in the first and second embodiments.

REFERENCE NUMERALS OR MARKS

1 upper mold; 1 a projection; 2 lower mold; 3 intermediate product; 3 aboss; 3 b discoid; 3 c cylindrical thick wall; 4 hole; 5 disk; 6 wheel;7 spoke; 8 rim; 9 depression; 13 waste hole; 18 pre-wheel; 19 to-be-rimpart; 20 to-be-disk part; 21 lower mold; 22 upper mold; 23 intermediateproduct; 29 light alloy; 30 press device; 33 guide rail; 35 mountingbase; and 39 bed.

DETAILED DESCRIPTION OF THE INVENTION

Used as a starting piece is an intermediate product integrally having; ato-be hub projection at center, a discoid surrounding the to-be hubprojection, and the to-be rim part of a cylindrical thick wall. Thediscoid is portion-by-portion-wise successively pressed by a tool havingprojections and some metal is punched out to form a disk-part pattern.Then, spinning processing is made on the hollow cylinder as to completea wheel having a disk of 17 inch or more diameters.

EMBODIMENT 1

FIG. 1( a) is a vertical sectional view schematically showing anintermediate product and molds, which are used for the invention-wiserotational forging. Numeral 1 designates the upper mold that movesupward and downward in vertical direction. Numeral 2 designates thelower mold that is mounted on a bed 39 rotated by not-illustrateddriving device and controlled as to repeat rotation by certain angle andsubsequent stopping. Numeral 3 designates intermediate product formed oflightweight alloy of; aluminum, magnesium or the like. The intermediateproduct has a to-be-hub boss 3 a, a discoid 3 b around the boss, and acylindrical thick wall 3 c around the discoid for forming a rim. Thoughnot illustrated, the intermediate product and the molds are heated byburners at around the molds so as to be maintained at a temperaturerange of 420 through 450° C., at which the intermediate product easilyundergo a plastic deformation. The upper mold 1 having projections 1 amoves downward by a predetermined distance and thus presses the discoid3 b to form a disk pattern comprised of holes or recesses.

FIG. 1( b) is a vertical sectional view showing a state the upper mold 1moves down and the projections 1 a punches the discoid 3 b. Metal piecestaken out by the punching move into the recesses 2 a. The recesses maybe replaced by holes as indicated by broken lines. The depth-wisedistance the projections 1 a push out on or through the discoid 3 b isabout 2 through 5 mm at every pressing motion. After retreating of theupper mold, the lower mold rotates by one pitch of the disk pattern andthen stopped. Thereafter, the upper mold moves down again as to pressdown on or through portions of the discoid by the predetermineddepth-wise distance. Such processing is repeated as to form a diskpattern comprised of the holes that are punched out by the pressing.FIG. 1( c) is a vertical sectional view showing the intermediate product3′ after forming the holes 4 on the discoid.

FIG. 2( b) shows an example of a wheel 6 and its pattern on the disk 5,where punching or pressing on portion of the disk has been made byprojections 1 a and 1 b. The projections may be formed not only on oneportion of the disk but also on a plurality of portions of the disk sofar as the capacity of the press device allows. Conversely, if capacityof the press device is insufficient for forming a portion of thepredetermined pattern by one pressing, molds of a plurality of kinds areused by successive changing of the molds, as to step-by-step-wiseachieving clearer and clearer hole or recess pattern on such a portion.

FIG. 2( a) is a perspective view of the upper mold seen from below,which has two pair of projections in a centrosymmetry arrangement as twodifferent projections are arranged to be adjacent with each other. Bysuch configuration of the mold, balancing is easily achieved andproduction efficiency is enhanced to be two-folded.

One of the two pair of the projections 1 a are for holes 4 a on the disk5, and the other projections 1 b are for other holes 4 b. Because thepressing is made to every pitch of the pattern contrary to en blocpressing on whole of the discoid 3 b, bulging up on spokes 7 (please seeFIG. 2( b)) is expected to be slight. Thus, the thickness of the disk isalmost equal to depth-wise dimension of the spokes. Nevertheless, filetsin a manner of wrought surface texture may be formed on upper faces ofthe spokes. Whereas the intermediate product shown in FIG. 1( a) isproduced by either of forging and casting, forged one has more denselypacked metallographic structure and higher mechanical strength. Thus,smaller thickness of the disk may be adopted when the forged one isadopted. After forming the holes on the discoid, cutting is made onreverse side of the discoid as to complete the disk.

Typical one of the lightweight-metal wheel has holes on areas other thanthe spokes, thus area or range of the pressing may be classified intotwo categories as shown in FIG. 3. The disk 5 has; the Y-shaped spokes6, the holes 4 a and 4 b, and depressions 9 a and 9 b at along joint ofthe spokes with the rim 8. A range indicated by reference symbol of “B”encompasses one of the hole 4 a and two halves of the other kind ofholes 4 b as suggested by hatchings in the figure. When theportion-by-portion-wise forging is made by such range of the “B”, eachbranch of the spokes is sandwiched from both sides, thus a slightbulging up is made as to form an appearance of wrought surface texture.Holes are formed on areas having the hatching in the figure, thus suchpressing is preferred in making narrow ones of the spokes.

In a range indicated by reference symbol of “C”, spoke 7 a is sandwichedfrom both sides and spoke 7 b is free from such sandwiching. In this wayof portion-by-portion-wise forging, depth-wise stroke of each pressingmotion is set to be small as to avert deformation or distortion of thespokes, or in otherwise, the projections on the mold are configured suchthat punching is made almost vertically.

Apart from the example shown in the drawings, when the spokes themselvesare thick in plan view such as a case of 5-spokes wheel, extent ofdeformation or distortion of the spokes is small even when thedepth-wise stroke of pressing motion is large. Because successivepressing is made by successively rotating the lower mold, depth-wisestroke is suitable in a range of 2 through 5 mm, and is appropriatelyselected depending on shape of the spokes. The areas of pressing by onestroke of the upper mold are set to be slightly larger than thoseindicated by “B” or “C” as to press and flatten out impartialdistribution of the metal at seams between the areas of successivestrokes.

A way of forming the depressions 9 a and 9 b at around junctures of thespokes 7 with the rim 8 will be explained by use of FIGS. 4( a)-4(d).FIG. 4( a) is an elevational view of the disk in a final product. Holes4 a and 4 b have been already punched out, and a range of pressed by onestroke is indicated by “D” in the figure; and FIG. 4( d) shows a partialsection in the final product. The intermediate product at a stage toform the depressions 9 a and 9 b has a shape just after the punching outof the holes 4 a and 4 b and has leftover portions 9 remained after thepunching. At a time the forming is completed, bottoms 10 of thedepressions are inclined and tapered toward the holes.

Therefore, the metal of the leftover portions 9 has to be moved towardthe holes 4 a and 4 b. Thus, upper mold 11 having the projections 11 aas shown in FIG. 4( b) is repeatedly applied to press out the metal ofthe leftover portions 9 toward the holes 4 a and 4 b, so as to bedeformed to a state shown in FIG. 4( c). Then, upper mold 12 having theprojections 12 a as shown in FIG. 4( c) is applied as to form thedepressions 9 a and 9 b shown in FIG. 4( d). Simultaneously, the jointsof the spokes 7 with the rim 8 a are completed.

Various sectional shapes may be adopted for the joints. Inclined facesof the depressions 9 a and 9 b have a visual effect in that diameter ofthe disk appears to be large, has a structure of improving strength ofthe joints and the rims, and are used as faces for mounting an airvalve. In case of two-piece wheel, the inclined faces are used formounting fastener bolts for connecting the rim and disk parts. Shapingof the joints is not limited to the shown examples, and the face forinstalling the air valve may be on outer rim as to have a differentsectional view.

In an explanation made hereto, the holes in the disk pattern are formedas gradually enlarged in the portion-by-portion-wise forging.Nevertheless, the holes may be formed merely by the punching, dependingto the disk pattern. In such case, fillets are not formed on upper faceof the spokes, and thus, finishing processing is needed for removingburrs and chamfering or the like.

In another way of forming the holes by punching, waste holes 13 a and 13b are formed on beforehand as shown by the hatchings in the FIG. 5. Incase of the portion-by-portion-wise forging, when the projections on themold are applied on the discoid, the holes tend to become larger thanintended, by friction of drag of the metal. To cope with this, the wasteholes smaller than the predetermined holes are firstly formed bypunching machine, and then, the projections on the mold are abutted andpressed on the discoid. By this way, the metal tends to “flow” towardthe waste holes, and thereby, precision of the disk pattern is increasedand the required thrust force of the mold become smaller.

When processing in respect of the holes on the discoid and thus formingof the disk pattern are completed, the intermediate product is taken outfrom the lower mold. Then, spinning processing is made to theintermediate product as follows, as shown in FIG. 6. The intermediateproduct is held as sandwiched at the discoid by the mandrels 14 and 15and is rotated about center axis 17. In this state, a spinning roller 16is applied with pressing force as to form the rim 8 a and 8 b andcomplete the one-piece integral wheel.

EMBODIMENT 2

This embodiment is made by taking account the fact that the waste holesalleviate extent of thrust force of the upper mold, whereas it has beenmentioned that the waste holes 13 a and 13 b facilitate the “flow” ofthe metal in an explanation with respect to the FIG. 5.

In this embodiment, firstly, a pre-wheel 18 shown in FIG. 8( a) isformed by the portion-by-portion-wise forging from a billet formed oflightweight metal. The portion-by-portion-wise forging here is made in amanner that; the lower mold is rotated by a predetermined angle and thenstopped; subsequently, the upper mold moves down and presses a portionof the billet; and such process is repeated, as to expand the billet.

The pre-wheel 18 is disk-shaped and has a pre-rim 19 on its peripheryand a pre-disk 20 on center part. Subsequently, as shown in FIG. 8( b),waste holes 13 a and 13 b are punched out as to form a punched pre-wheel18 a.

FIG. 8( c) is a sectional view for indicating outline of the forgingprocess. The lower mold 21 has projections 21 a and 21 b for fitting thewaste holes 13 a and 13 b and has a recess 21 c for receiving adeforming portion at time of the pressing. The upper mold 22 has, on itspressing face, projections 22 a for pressing portions around the wasteholes, projections 22 b for forming the rim, and a projection 22 d forforming a screw hole at center of the disc. FIG. 8( d) is a sectionalview of the intermediate product 23 after the press forming. Detail ofthe press forming is explained below.

In a structure explained above, the upper mold 22 moves down with thelower mold 21 being held at fixed posture, and then inside or cavitybetween the molds is sealed off from the outside. The waste holes areexcluded from an area being pressed, thus, thrust force of the uppermold is alleviated by an areal ratio of the waste holes.

In case of a layout of Y-shaped spokes shown in FIG. 7, total area ofthe waste holes is about 25% of the overall area on front face of18-inch wheel. At a time the upper mold moves down and projections 22 a,22 b and 22 c begin to contact with the pre-wheel 18 a, the pre-wheel ispressed only at areas matching the projections, instead of whole face ofthe pre-wheel. Thus, sum of the areas is very small and less than 20% ofthe whole face.

Whereas en bloc pressing on whole face of the pre-wheel for 18-inchwheel requires the press device of 8000-ton capacity, the above mannerof the pressing is roughly estimated to merely require one having 20% ofthat; that is, the press device of 1600-ton capacity. In actual sense,the above manner of the pressing in this case requires the press deviceof 2000-ton capacity because some energy or thrust force is consumed forplastic deformation of the thrust-outing metal.

At a time the upper mold with its projections moves down to almost lowerend of its stroke, whole of the pre-wheel that has been deformed by theplastic thrust-out flow and include such thrust-out metal is pressed;thus, the press device of the 8000-ton capacity is appeared to berequired on first glance. Nevertheless, due to the alleviation by thewaste holes, at least 25% of the 8000-ton capacity is alleviated, thus,the press device of 6000-ton capacity is enough.

FIGS. 9( a)-9(d) are views for explaining a manner of forging in thisembodiment. FIG. 9( a) is a partial elevational view of a punchedpre-wheel 18 a that has the waste holes having been punched out. Thewaste holes are fitted with the projections 21 a and 21 b on the lowermold; and formed are to-be rim part 19 on periphery and to-be disk part20 on center part. Hatching in the FIG. 9( a) indicates an area on whichprojections on the upper mold presses.

FIGS. 9( b)-(d) are sectional views for a section indicated by A-A′ onthe FIG. 9( a) and show a manner of pressing the to-be disk part 20 bythe projections 22 a on the upper mold, which press portions around thewaste holes. On course of moving down of the upper mold, the to-be diskpart 20 gradually bulges up by the forging at a sealed-off state. Then,in a stage shown in FIG. 9( d), the projections do not contact with thelower mold as to leave marginal-thickness fins 20 a at lowest end of thestroke of the upper mold. The marginal-thickness fins are removed afterthe forging, by a lathe turning machine.

At a time of transition from a stage of FIG. 9( c) to a stage of FIG. 9(d), upper faces of the to-be rim part 19 and the to-be disk part 20 arerather similar with those of a wheel of completed product. Thus, in thistransition stage, almost whole area on the pre-wheel is pressed, andthereby, the press device of 6000-ton capacity is needed for the en blocforging as mentioned before. Nevertheless, when the press device of3000-ton capacity is used, the upper mold is divided to an appropriatenumber in accordance with repeating pattern on the mold; and the lowermold is fixes to be stationary after rotating a predetermined angle.Thereafter, thus divided upper mold is descended as to make thepressing. For example, the upper mold is divided to four blocks, two ofthem are symmetrically arranged and move down to press the partsindicated in the FIG. 9( a). Then, the lower mold is rotated by 45degree and then held in a fixed position, and thereafter, the pressingis repeated as to reach a state shown in FIG. 9( d).

In such way of the portion-by-portion-wise forging, transition to thestate of the FIG. 9( d) should be made step by step as to secureuniformity of the metallographic structure of the pre-wheel on course ofthe deformation. At a transition from a stage of FIG. 9( b) to a stageof FIG. 9( c), non-divided or integral one of the upper molds is used,and then divided ones are used at a transition from a stage of FIG. 9(c) to a stage of FIG. 9( d).

In the Embodiment 1 and the Embodiment 2, changing of the upper mold isneeded. By use of FIG. 10, an easy way of the changing will be explainedbelow. At lower end of the vertically driving mechanism of the pressdevice 30, a guide rail(s) 33 are arranged in a horizontal direction.Several ones of the upper molds (two in the figure) are mounted on lowerface of mounting base 35 that has traveling rollers 34, as to run alongthe guide rail(s) 33. The mounting base 35 is moved by a drive mechanism36 for generating a thrusting power such as a hydraulic cylinder or amotor, so as to change the upper mold 31.

When positioning pin 37 on the press device 30 fits into a firstlatching recess 38 a formed on the mounting base 35, first upper mold 31is located over the lower mold 32. When positioning pin 37 on the pressdevice 30 fits into a second latching recess 38 b on the mounting base35, second upper mold 31 is located over the lower mold 39.

When a lightweight metal body 29 is subjected to hot forging by use ofthe first and second upper molds and changing the upper molds in amanner as above, the changing of the upper mold is made in a short time.Thus, no reheating of the pre-wheel 18 a or the like is needed atoccasions of changing the molds, so that forging on the lightweightmetal body 29 is made without interruption or pause.

The lightweight metal body 29 may be solid cylindrical billet, theintermediate product 3 of the Embodiment 1, the pre-wheel 18 a of theEmbodiment 2, or the like. The bed 39 has a mechanism for rotating thelower mold by a predetermined angle and then fixing the lower mold to bestationary.

INDUSTRIAL APPLICABILITY

Portion-by-portion-wise forging method of present invention enablesforming of large-diameter disk by use of a small-scale press device, andthus decreasing equipment or facility cost and simplifying the molds.Moreover, surfaces of the disk pattern make wrought face, and hence,wheel product is by no means inferior to that formed by the en blocforging by use of a large-scale press device.

1. A method of manufacturing a vehicle's wheel formed of lightweightmetal, comprising; preparing a first forming tool, which has on apressing face thereof, recesses or holes that are arranged in arotational symmetry of predetermined angle around a center axis, saidfirst forming tool further including an annular recess; preparing asecond forming tool, which has on its pressing face, one or moreprojections only within a certain angular region about a correspondingcenter axis; preparing an intermediate product by casting or forging soas to integrally form at least a center part and a discoid part, whichrespectively correspond to a hub and a disk of the wheel, said castingor forging further forming a cylindrical tube of thick wall whichcorresponds to a rim of the wheel, said cylindrical tube of thick wallbeing integrally formed with said center part and said discoid part ofthe intermediate product; heating the intermediate product to aplasticity temperature; placing the intermediate product so as to beheld coaxially on the first forming tool, the cylindrical tube beingreceived in said annular recess of the first forming tool; positioningthe second forming tool relative to the first forming tool, so as to becoaxial with the first forming tool and so that each of the projectionsis positioned to match one of said recesses or holes; pressing a portionof the discoid part by thrusting the second forming tool relative to thefirst forming tool as to punch out one or more holes on the portion ofthe discoid part or to forge the portion of the discoid part; retreatingthe second forming tool relative to the first forming tool, after thepressing; rotating the first forming tool around its center axis by saidpredetermined angle, relative to the second forming tool, after theretreating; and repeating the pressing, the retreating and the rotating,until said pressing is made for every one of said recesses or holes onthe first forming tool.
 2. A method of manufacturing a vehicle's wheelaccording to claim 1, further comprising; preparing a third forming toolwhich has, on its pressing face, one or more projections only within acertain angular region about a center axis thereof; positioning thethird forming tool relative to the first forming tool, so as to becoaxial with the first forming tool and so that each of the projectionsis positioned to match an adjacency of one of said recesses or holes;pressing a portion of the discoid part by thrusting the third formingtool relative to the first forming tool so as to forge said adjacency ofone or more of said recesses or holes; retreating the third forming toolrelative to the first form, after the pressing; rotating the firstforming tool around said center axis thereof by said predeterminedangle, relative to the third forming tool, after the retreating; andrepeating of the pressing, the retreating and the rotating, until saidpressing is made on said each adjacency for every one of said recessesor holes on the first forming tool.
 3. A method of manufacturing avehicle's wheel according to claim 2, further comprising: finishing witha fourth forming tool that has projections, each of which corresponds toone of the projections of the third forming tool, so as to finish apattern of holes on the disk and depressions on a rim of the wheel.
 4. Amethod of manufacturing a vehicle's wheel according to claim 1, furthercomprising: providing waste holes on the discoid part of theintermediate product before said placing, as arranged in a rotationalsymmetry of said predetermined angle around a center axis of theintermediate product; wherein each of the waste holes is smaller than acorresponding one of said recesses or holes, and is positioned to matchthe corresponding one of said recesses or holes at a time of saidpositioning.
 5. A method of manufacturing a vehicle's wheel according toclaim 1, wherein ridges of said projections on the second forming tool,which are for punching the holes on the discoid part, are shaped assharp-angled in a sectional view along the center axis, at a 90 degreeor sharper angle.
 6. A method of manufacturing a vehicle's wheelaccording to claim 5, wherein a distal end surface of each of saidprojections is shaped as concave so that said ridges of the projectionsare shaped as sharp-angled at an angle less than 90 degrees.